1. Field of the Invention
This application claims the priority of Japanese Patent Application 2008-89251 filed on Mar. 31, 2008, the teachings of which are incorporated herein by reference in their entirety. This invention relates to the manufacturing process of the electrodes for electrolysis to be applied for various kinds of electrolysis for the industrial purpose, especially relating to the manufacturing process of the electrodes for electrolysis with high durability in electrolysis for the industrial purposes including electrolysis copper foil manufacturing, aluminum electrolysis capacitor manufacturing by a liquid power feeding, and continuous galvanized iron sheet manufacturing, which is associated with oxygen generation at the anode.
2. Description of the Related Art
Recent electrolysis processes for the industrial purposes including electrolysis copper foil manufacturing, aluminum electrolysis capacitor manufacturing by a liquid power feeding, and continuous galvanized iron sheet manufacturing involve oxygen generation at the anode and therefore, anodes of metal titanium substrate coated with iridium oxide as electrode catalyst are widely applied for its high resistance to oxygen generation. In this type of electrolysis for the industrial purposes which involves oxygen generation at the anode, however, organic substance or impurity elements are added for stabilization of products, which causes various electrochemical and chemical reactions. These reactions may result in higher consumption of electrode catalyst due to an increased concentration of hydrogen ions (lower pH value) associated with oxygen generation. With electrode catalyst of iridium oxide, popularly applied for the case of oxygen generation, electrode consumption is considered to start from consumption of itself and concomitantly occurring corrosion of the electrode substrate by the same reason, and as a result of partial and internal consumption and detachment of electrode catalyst, electric current flows intensively onto remaining part of the electrode catalyst, and thus catalyst consumption proceeds continuously at accelerating pace.
Conventionally, in order to suppress corrosive dissolution of the electrode substrate and successive detachment of effective electrode catalyst from the electrode substrate, various processes are applied, typically such as installing an interlayer between the titanium substrate and the electrode catalyst layer. Such interlayer is selected to have an electrode activity lower than that of electrode catalyst layer and electron conductivity, designed to have a role to alleviate damages of the substrate by isolating the electrode substrate away from the oxygen generation area which causes corrosive electrolyte and lowered pH. As the interlayers satisfying these conditions, various processes are described in the patent documents shown below.
In Patent Document 1, an interlayer provided with tantalum and/or niobium oxide in a thickness between 0.001 g/m2 and 1 g/m2 as metal and provided with conductivity across the titanium oxide coating formed on the substrate surface was suggested.
In Patent Document 2, a valence-controlled semiconductor with oxides of tantalum and/or niobium added to oxides of titanium and/or tin was suggested. The processes described in Patent Document 1 and Patent Document 2 have been widely applied industrially.
In Patent Document 3, a metal oxide interlayer formed on an undercoating layer comprising amorphous layer without grain boundary on the substrate surface prepared by vacuum sputtering was suggested.
Recently, however, reflecting demand for high economic efficiency, operation conditions have grown more and more stringent and highly durable electrodes are requested. Under these circumstances, the processes to prepare an interlayer as described in Patent Documents 1-3 have not achieved sufficient effects desired.
In order to solve the problems associated with the preparation of interlayers in Patent Documents 1-3, a method to form an interlayer comprising a single layer of titanium oxide where a titanium electrode substrate itself is electro-oxidized so that the surface titanium on said electrode substrate is transformed into titanium oxide is disclosed in Patent Document 4.
With the electrode described in Patent Document 4, the interlayer formed by electro-oxidation is extremely thin to provide sufficient corrosion resistance; therefore, on the surface of said first interlayer prepared by electro-oxidization, the second thick titanium oxide single layer is additionally formed by thermo-decomposition process, on which the electrode catalyst layer is configured. However, the method described in Patent Document 4 is poor in workability, less economical, and not practical since it requires two processes, of works in preparing the interlayer; more specifically, electro-oxidization and thermo-decomposition, which require two completely different equipment and machinery.
In Patent Document 5, a highly corrosion resistant, dense interlayer which is able to tightly bond with the electrode substrate, comprising high-temperature oxide coating prepared by high-temperature oxidation treatment of the electrode substrate between the electrode substrate and the electrode catalyst was suggested.
According to Patent Document 5, the oxide coating prepared by high temperature oxidation of the electrode substrate is highly corrosion resistant and dense, and tightly bonded with the electrode substrate, thus protecting the electrode substrate and enabling to sufficiently support electrode catalyst comprising mainly oxides, through oxide-oxide bonding.
In Patent Document 6, an interlayer with a double-layered structure to further enhance the effects of the method in Patent Document 5, comprising metal oxide and high temperature oxide coating derived from the substrate by high temperature oxidation was suggested.
However, either of the methods by Patent Document 5 and Patent Document 6 is inadequate to form a highly corrosion resistant, dense interlayer enabling to tightly bond with the electrode substrate between the electrode substrate and the electrode catalyst and could not obtain electrodes for electrolysis with enhanced density, electrolytic corrosion resistance and conductive property.
[Patent Document 1] Japanese Patent Application Publication No. JP 60-21232 (B Patent Gazette) also published as Japanese Patent Application Publication No. JP 57-192281 A)
[Patent Document 2] Japanese Patent Application Publication No. JP 60-22074 (B Patent Gazette) also published as Japanese Patent Application Publication No. JP 59-038394 A)
[Patent Document 3] Japanese Patent Application Publication No. JP 2761751 (B Patent Gazette) also published as Japanese Patent Application Publication No. JP 2-247393 A)
[Patent Document 4] Japanese Patent Application Publication No. JP 7-90665 (A Patent Gazette)
[Patent Document 5] Japanese Patent Application Publication No. JP 2004-360067 (A Patent Gazette)
[Patent Document 6] Japanese Patent Application Publication No. JP 2007-154237 (A Patent Gazette)